Inkjet imaging devices eject liquid ink from printheads to form images on an image receiving surface. The printheads include a plurality of inkjets that are arranged in some type of array. Each inkjet has a thermal or piezoelectric actuator that is coupled to a printhead controller. The printhead controller generates firing signals that correspond to digital data for images. The frequency and amplitude of the firing signals correspond to the selective activation of the printhead actuators. The printhead actuators respond to the firing signals by expanding into an ink chamber to eject ink drops onto an image receiving member and form an ink image that corresponds to the digital image used to generate the firing signals.
FIG. 4 illustrates a prior art high-speed aqueous ink image producing machine or printer 10. As illustrated, the printer 10 is a printer that directly forms an ink image on a surface of a web W of media pulled through the printer 10 by the controller 80′ operating one of the actuators 40 that is operatively connected to the shaft 42 about which a take up roll 46 is mounted. The printhead modules can be configured to have only one printhead that has a width that corresponds to a width of the widest media in the cross-process direction that can be printed by the printer or the printhead modules can be configured with a plurality of printheads with each printhead having a width that is less than a width of the widest media in the cross-process direction that the printer can print. In these modules having multiple printheads, the printheads are arranged in an array of staggered printheads that enables media wider than a single printhead to be printed. Additionally, the printheads can also be interlaced so the density of the drops ejected by the printheads in the cross-process direction can be greater than the smallest spacing between the inkjets in a printhead in the cross-process direction. A printhead module is provided for each color used by the printer 10.
After an ink image is printed on the web W, the image passes under an image dryer 30. The image dryer 30 can include an infrared heater, a heated air blower, air returns, or combinations of these components to heat the ink image and at least partially fix an image to the web. An infrared heater applies infrared heat to the printed image on the surface of the web to evaporate water or solvent in the ink. The heated air blower directs heated air over the ink to supplement the evaporation of the water or solvent from the ink. The air is then collected and evacuated by air returns to reduce the interference of the air flow with other components in the printer.
As further shown, the media web W is unwound from a roll of media 38 as needed by controller 80 operating one or more actuators 40 to rotate the shaft 42 on which the take up roll 46 is placed to pull the web from the media roll 38 as it rotates about the shaft 36. When the web is completely printed, the take-up roll can be removed from the shaft 42 for additional processing. Alternatively, the printed web can be directed to other processing stations (not shown) that perform tasks such as cutting, collating, binding, and stapling the media.
Operation and control of the various subsystems, components and functions of the machine or printer 10 are performed with the aid of a controller or electronic subsystem (ESS) 80. The ESS or controller 80 is operably connected to the components of an ink delivery system 20, a purge system 24, the printhead modules 34A-34D (and thus the printheads), actuators 40, heater 30, and a user interface 50. In operation, image data for an image to be produced are sent to the controller 80 from either a scanning system or an online or work station connection for processing and generation of the printhead control signals output to the printhead modules 34A-34D. Additionally, the controller 80 determines and accepts related subsystem and component controls, for example, from operator inputs via the user interface 50, and accordingly executes such controls. As a result, aqueous ink for appropriate colors are delivered to the printhead modules 34A-34D. Additionally, pixel placement control is exercised relative to the surface of the web to form ink images corresponding to the image data, and the media can be wound on the take-up roll or otherwise processed.
Using like numbers for like components, a prior art ink delivery system 20 used in printer 10 is shown in FIG. 5. The ink delivery system 20 includes an ink supply reservoir 604 that is connected to a printhead 608 and is positioned below the printhead so the ink level can be maintained at a predetermined distance D below the printhead to provide an adequate back pressure on the ink in the printhead. This back pressure helps ensure good ink drop ejecting performance. The ink reservoir is operatively connected to a source of ink (not shown) that keeps the ink at a level that maintains the distance D. The printhead 608 has a manifold that stores ink until an inkjet pulls ink from the manifold. The capacity of the printhead manifold is typically five times the capacity of all of the inkjets. The inlet of the manifold is connected to the ink reservoir 604 through a conduit 618 and a conduit 634 connects the outlet of the manifold to a waste ink tank 638. A valve 642 is installed in the conduit 634 to selectively block the conduit 634. A valve 612 is also provided in the conduit 614 connecting an air pressure pump 616 to the ink reservoir 604 and this valve remains open to vent the reservoir to atmosphere except during purging operations.
When a new printhead is installed or an incident occurs, such as an ink reservoir repair or replacement of an ink supply tube, air or air bubbles can exist in the conduit 618 or the manifold of the printhead. To clear the air and prime the supply lines and printhead with ink, a manifold purge is performed. In a manifold purge, the controller 80 operates the valve 642 to enable fluid to flow from the manifold outlet to the waste ink tank 638, activates the air pressure pump 616, and operates the valve 612 to close the ink reservoir to atmospheric pressure so pump 616 can pressurize the ink in the ink reservoir 604. The pressurized ink flows through conduit 618 to the manifold inlet of printhead 608. Because valve 642 is also opened, the pneumatic impedance to fluid flow from the manifold to the inkjets is greater than the pneumatic impedance through the manifold. Thus, ink flows from the manifold outlet to the waste tank. The pressure pump 616 is operated at a predetermined pressure for a predetermined period of time to push a volume of ink through the conduit 618 and the manifold of the printhead 608 that is sufficient to fill the conduit 618, the manifold in the printhead 608, and the conduit 634 without completely exhausting the supply of ink in the reservoir. The controller then operates the valve 642 to close the conduit 634 and operates the valve 612 to vent the ink reservoir to atmospheric pressure. Thus, a manifold purge fills the conduit 618 from the ink reservoir to the printhead, the manifold, and the conduit 634 so the manifold and the ink delivery system are primed since no air is present in the conduits or the printhead. The ink reservoir is then resupplied to bring the height of the ink to a level where the distance between the level in the reservoir and the printhead inkjets is D, as previously noted.
To prime the inkjets in the printhead 608 following a manifold prime, the controller 80 closes the valve 612 and activates the air pressure pump 616 to pressurize the head space of the reservoir 604 to send ink to the printhead. Because the valve 642 is closed, the pneumatic impedance of the primed system through the manifold is greater than the pneumatic impedance through the inkjets so ink is urged into the inkjets. Again, the purge pressure is exerted at a predetermined pressure for a predetermined period of time to urge a volume of ink into the printhead that is adequate to fill the inkjets. Any ink previously in the inkjets is emitted from the nozzles in the faceplate 624 of the printhead 608. This ink purging primes the inkjets and can also help restore clogged and inoperative inkjets to their operational status. After the exertion of the pressure, the controller 80 operates the valve 612 to open and release pressure from the ink reservoir. A pressure sensor 620 is also operatively connected to the pressure supply conduit 622 and this sensor generates a signal indicative of the pressure in the reservoir. This signal is provided to the controller 80 for regulating the operation of the air pressure pump. If the pressure in the reservoir during purging exceeds a predetermined threshold, then the controller 80 operates the valve 612 to release pressure or reduce the output of the pressure source 616. If the pressure in the reservoir drops below a predetermined threshold during purging, then the controller 80 operates the pressure source 616 to raise the pressure. The two predetermined thresholds are different so the controller can keep the pressure in the reservoir in a predetermined range during purging rather than at one particular pressure.
When new printheads are being installed in a printer or supply lines are being replaced, the manifold purge described above can force air into the inkjets in some situations. If air enters too many inkjets, then the operational status of the printhead can be adversely affected. This condition is particularly important for some types of printheads that more easily trap air bubbles in the inkjets of a printhead than some other types of printheads. The capacity of the ink reservoir 604 sometimes presents an issue as well as the reservoir can be exhausted before the conduits are primed and that exhaustion brings air into the ink delivery system. The amount of ink that needs to be pushed to the waste tank to purge the system of air can be enough to render inkjets in the printhead inoperable and the printhead may need to be subjected to a recovery procedure, which may last as long as twelve hours. Enabling a priming procedure that fills the supply lines and waste ink lines with ink before the insertion of the printheads into the ink delivery system would be beneficial.